Enhanced RS-232 Line Drivers/Receivers

Transcription

1 SP232A Enhanced RS-232 Line Drivers/Receivers FEATURES Operates from a Single 5V Power Supply Meets all RS-232F and ITU V.28 Specifications Operates with 0.1μF Ceramic Capacitors High Data rat 120kbps under load Low power CMOS Operation /-2kV Human Body Model ESD Protection Lead Free packaging available DESCRIPTION The SP232A is a line driver and receiver pair that meets the specifications of RS-232 and V.28 serial protocols. This device is pin-to-pin compatible with popular industry standard pinouts. The SP232A offers 120kbps data rate under load, small ceramic type 0.1μF charge pump capacitors and overall ruggedness for comercial applications. The SP232A features Exar's BiCMOS design allowing for low power operation without sacrificing performance. This device is avaialble in plastic DIP, SOICW and nsoic packages operating over the commercial and industrial temperature ranges.

2 These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below are not implied. Exposure to absolute maximum ratings conditions for extended periods of time may affect reliability. Supply Voltage (VCC)... 6V V... (Vcc-0.3V) to 11.0V V V Input Voltages Tin V to (Vcc 0.3V) Rin.../-15V Output Voltages Tout...(V, 0.3V) to (V-, -0.3V Rout V to (Vcc 0.3V) Absolute Maximum Ratings Short Circuit duration Tout...Continuous Package Power Dissipation: Plastic DIP...375mW (derate 7mW/ C above 70 C) Small Outline...375mW (derate 7mW/ C above 70 C) Storage Temperature C to 150 C Lead Temperature (soldering, 10s) C ELECTRICAL CHARACTERISTICS Vcc=5V ±10%, 0.1μF charge pump capacitors, Tmin to Tmax, unless otherwise noted, Typical values are Vcc=5V and Ta=25 C PARAMETER TEST CONDITIONS MIN TYP MAX UNIT TTL INPUT Logic Threshold LOW TIN 0.8 Volts Logic Threshold HIGH TIN 2.0 Volts Logic Pull-Up Current TIN = 0V μa TTL OUTPUT Output Voltge LOW Iout = 3.2 ma: Vcc = 5V 0.4 Volts Output Voltage HIGH Iout = -1.0 ma 3.5 Volts RS-232 OUTPUT Output Voltage Swing All Transmitter outputs loaded with 3k ohms to GND /-5.0 /-6.5V Volts Output Resistance Vcc = 0V, Vout = /-2V 300 Ohms Output Short Circuit Current Infinite Duration /-18 ma Maximum Data Rate CL = 2500pF, RL = 3kΩ kbps RS-232 INPUT Voltage Rang15 15 Volts Voltage Threshold LOW Vcc = 5V, Ta=25 C Volts Voltage Threshold HIGH Vcc = 5V, Ta=25 C Volts Hysteresis Vcc = 5V, Ta=25 C Volts Resistance Ta=25 C, -15V Vin 15V kω 2

3 ELECTRICAL CHARACTERISTICS Vcc=5V ±10%, 0.1μF charge pump capacitors, Tmin to Tmax, unless otherwise noted, Typical values are Vcc=5V and Ta=25 C DYNAMIC CHARACTERISTICS Driver Propagation Delay TTL to RS_232; CL = 50pF μs Receiver Propagation Delay RS-232 to TTL, μs Instantaneous Slew Rate CL = 10pF, RL = 3-7kΩ 30 V/ μs Transition Region Slew Rate POWER REQUIREMENTS CL = 2500pF, RL = 3kΩ; Measured from 3V to -3V or -3V to 3V 10 V/ μs Vcc Power Supply Current No Load, Vcc = 5V, Ta=25 C ma Vcc Power Supply Current, Loaded All Transmitters RL = 3kΩ, Ta=25 C 11 ma PIN ASSIGNMENTS Pin Number Pin Name Pin Function 1 C1 Positive terminal of the voltage doubler charge pump capacitor 2 V 6.5V generated by the charge pump 3 C1- Negative terminal of the voltage doubler charge pump capacitor 4 C2 Positive terminal of the inverting charge pump capacitor 5 C2- Negative terminal of the inverting charge pump capacitor 6 V- -6.7V generated by the charge pump 7 T2OUT RS-232 driver output 8 R2IN RS-232 receiver input 9 R2OUT TTL/CMOS receiver output 10 T2IN TTL/CMOS driver input 11 T1IN TTL/CMOS driver input 12 R1OUT TTL/CMOS receiver output 13 R1IN RS-232 receiver input 14 T1OUT RS-232 driver output 15 GND Ground 16 Vcc 5V supply voltage 3

4 DETAILED DESCRIPTION The SP232A transceiver is a two driver and two receiver device that meets the EIA/TIA- 232 and V.28 serial communication protocol. The device is pin-to-pin compatible with popular industry standard pinouts. The SP232A offers 120kbps data rate, 10V/μs slew rate and a regulated charge pump that operates from a single 5V supply. The proprietary on-board charge pump generates a regulated output of /-6.5V for RS- 232 compliant voltage levels. Theory Of Operation The SP232A is made up of three basic circuit blocks: 1. Driver, 2. Receiver, and 3. charge pump. Drivers The drivers are inverting level transmitters that convert TTL or CMOS logic levels to EIA/TIA- 232 levels with an inverted sense relative to the input logic levels. Typically, the RS-232 output voltage swing is /-6.5V with no load and /- 5.0V minimum when fully loaded. The driver outputs are protected against infinite short-circuits to ground without degradation in reliability. The drivers can guarantee output data rates of 120Kbps under worst case loading of 3k ohms and 2500pF. The driver output Slew Rate is internally limited to 30V/μs in order to meet the EIA standards (EIA-232F). Additionally, the driver output LOW to HIGH transition meet the monotonicity output requirements of the standard. Receivers The receivers convert EIA/TIA-232 signal levels to TTL or CMOS logic output levels. Since the input is usually from a transmission line, where long cable length and system interference can degrade the signal, the receiver inputs have a typical hysteresis margin of 500mV. This ensures that the receiver is virtually immune to noisy transmission lines. Should a input be left unconnected, an internal 5Kohm pull-down resistor to ground will commit the output of the receiver to a logic HIGH state. The input voltage range for the SP232A Receiver is /-15V. DESCRIPTION Charge pump The charge pump is a patented design and uses a unique approach compared to older less efficient designs. The charge pump requires 4 external capacitors and uses a four phase voltage shifting technique. The internal power supply consists of a regulated dual charge pump that provides output voltages of /-6.5V. This is important to maintain compliant RS-232 levels regardless of power supply fluctuations. The charge pump operates in a discontinous mode using an internal oscillator. If the voltages are less than a magnitude of 6.5V, the charge pump is enabled. If the output voltage exceed a magnitude of 6.5V then the charge pump is disabled. The internal oscillator controls the four phases of the voltage shifting. A description of each phase follows: Phase 1 Vss charge store and double: The positive terminals of capacitors C1 and C2 are charged from Vcc with their negative terminals initially connected to ground. C1 is then connected to ground and the stored charge from C1- is superimposed onto C2-. Since C2 is still connected to Vcc the voltage potential across C2 is now 2 x Vcc. Phase 2 Vss transfer and invert: Phase two connects the negative terminal of C2 to the Vss storage capacitor and the positive terminal of C2 to ground. This transfers the doubled and inverted (V-) voltage onto C4. Meanwhile, capacitor C1 is charged from Vcc in order to prepare it for its next phase. Phase 3 Vdd charge store and double: Phase three is identical to the first phase. The positive terminals of C1 and C2 are charged from Vcc with their negative terminals initially connected to ground. C1 is then connected to ground and the stored charge from C1- is superimposed onto C2-. Since C2 is still connected to Vcc the voltage potential across capacitor C2 is now 2 x Vcc. 4

5 Phase 4 Vdd transfer. The fourth phase connects the negative terminal of C2 to ground and the positive terminal of C2 to the Vdd storage capacitor. This transfers the doubled (V) voltage onto C3. Meanwhile, capacitor C1 is charged from Vcc to prepare it for its next phase. Under lightly loaded conditions, the intelligent pump oscillator maximizes efficiency by running only as needed to maintain V and V- voltage levels. Since interface transceivers spend most of their time at idle, this power-efficient innovation can greatly reduce total power consumption. This improvement is made possible by the independent phase sequences of the Exar charge pump design. DESCRIPTION The clock rate of the charge pump typically operates greater than 70kHz allowing the pump to operate efficiently with small 0.1uF capacitors. Efficient operation depends on rapid charging and discharging of C1 and C2. Therefore, the capacitors should be mounted as close as possible to the IC and have a low ESR (equivalent series resistance). Inexpensive, surface mount ceramic capacitors are ideal for use on charge pump. If polarized capacitors are used the positive and negative terminals should be connected as shown on the typical operating circuit. A diagram of the 4 individual phases is shown in Figure 1. V CC - Phase 2 Vss transfer from C2 to C4. Meanwhile C 1 is charged to Vcc V CC - Phases 1 and 3: Store/Double. Double charge from C 1 onto C2. C 2 is now charged to -2xVcc C C 1 2 Vss V C 3 C 4 C C 1 2 V V- C 3 C 4 Patented 5,306,954 V CC - Phase 4 VDD transfer from C2 to C3. Meanwhile C1 is charged to Vcc C C 1 2 V DD e e V V- C 3 C 4 Figure 1. Charge pump phases 5

6 TYPiCAL PERFoRMAnCE CHARACTERiSTiCS Figure 2, Charge pump waveforms with no load ( = C, 2 = C2, 3 = V, 4 = V-). Figure 5, Charge pump outputs at start up ( = Vcc, 2 = V, 3 = V-). Figure 3, Charge pump waveforms when fully loaded with 3k ohms ( = C, 2 = C2, 3 = V, 4 = V-). Figure 6, Typical Application circuit Figure 4, Loopback results at 60kHZ and 2500pF load ( = TXin, 2 = TXout/RXin, 3 = RXout). Exar Corporation Kato Road, Fremont CA, (50) Fax (50) SP232A_00_

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10 ORDERING INFORMATION Part number LEAD FREE Tape & Reel Temperature range Package Type SP232ACN -L /TR From 0 to 70 0 C 16 pin nsoic SP232ACT -L /TR From 0 to 70 0 C 16 pin WSOIC SP232ACP -L /TR From 0 to 70 0 C 16 pin PDIP SP232AEN -L /TR From -40 to 85 0 C 16 pin nsoic SP232AET -L /TR From -40 to 85 0 C 16 pin WSOIC SP232AEP -L /TR From -40 to 85 0 C 16 pin PDIP All packages are available as lead free (RoHS compliant). To order add -L suffix to part number. For Tape and Reel add /TR. Reel quantity is 2,500 for NSOIC. Example: SP232ACN-L/TR = lead free and Tape and Reel. SP232ACN/TR = standard with Tape and Reel. Notice EXAR Corporation reserves the right to make changes to any products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no representation that the circuits are free of patent infringement. Charts and schedules contained herein are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writting, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized ; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2008 EXAR Corporation Datasheet May 2008 Send your Interface technical inquiry with technical details to: customersupport@exar.com Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. 10